1. Field of the Invention
The present invention relates to an air conditioning device for a vehicle for controlling temperature of a vehicle cabin at the time of heating by ON-OFF control of a hot water valve. More particularly, it relates to a heating unit of the air conditioning device for a vehicle which provides a comfortable air conditioning by keeping temperature of air diffused around a passenger's feet at more than a predetermined level.
2. Description of the Prior Art
In a heating unit for a vehicle, generally, control of temperature in a vehicle cabin has been performed by operating a hot water valve for controlling a flow rate of hot water, obtained by utilizing cooling water for cooling an engine, which passes through a coiled pipe for hot water, and an air-mix damper for controlling a volume of air passing through the space in the coiled pipe as described, for instance, in U.S. Pat. No. 4,356,705. However, the operations described above have hindered a precise temperature control of the vehicle cabin for the reason that positions of the valve and the damper to obtain a comfortable temperature condition vary dependent on changes in the weather and the load required to heat the interior of a vehicle where one of more passengers get on, with the result that it is difficult to keep the vehicle cabin at a uniform comfortable temperature. For this, the passengers having an uncomfortable feeling have been obliged to adjust the positions of the valve and the damper to control temperature in the vehicle cabin.